Astigmatism

Astigmatism, a visual defect due to the reflecting media of the eye not being of equal power in all meridians. Thus, rays in a vertical plane may be brought to a focus before those in a horizontal plane, or vice versa, and consequently the two sets of rays are not capable of being simultaneously focussed on the retina, and blurred images are therefore formed. A slight degree of astigmatism is present in almost all eyes, but sometimes the defect is so pronounced as to seriously interfere with accurate vision, and in that case it is most important that the condition should as far as possible be remedied by the use of suitable glasses.